title: Mapping of amide, amine, and aliphatic peaks in the CEST spectra of murine xenografts at 7 T.
abstract: OBJECTIVE
  To evaluate the performance of endogenous chemical exchange saturation transfer (CEST) spectra and derived maps in a longitudinal study of tumor xenografts to ascertain the role of CEST parameters in describing tumor progression and in distinguishing between tumor, muscle, and necrosis.
  
  
  METHODS
  CEST spectra of 24 mice with tumor xenografts (20 LLC and 4 MDA) were acquired at three time-points. We employed a novel method of decomposing the CEST spectrum into a sum of four Lorentzian shapes, each with a corresponding measured amplitude, width and frequency offset. This semi-quantitative method is an improvement over techniques which simply assess the asymmetry in the spectrum for the presence of CEST, due to the fact that it is not confounded by CEST peaks on opposing sides of the direct effect. The CEST images were compared to several other commonly employed contrast mechanisms: T1 relaxation, T2 relaxation, diffusion (ADC), and magnetization transfer (MT).
  
  
  RESULTS
  Tumor spectra had distinct CEST peaks corresponding to the presence of hydrogen exchange between free water and amide, amine, and aliphatic groups. All three CEST peaks (amide, amine, and aliphatic) were larger in the tumor tissue as compared with the adjacent healthy muscle.
  
  
  CONCLUSIONS
  CEST contrast (particularly the amine peak amplitude) performed especially well in distinguishing areas of apoptosis and/or necrosis from actively progressing tumor, as validated by histology.
authors.affiliation: Department of Medical Biophysics, University of Toronto, Toronto, Canada.
authors.forename: Kimberly L
authors.initials: KL
authors.lastname: Desmond
authors.forename: Firas
authors.initials: F
authors.lastname: Moosvi
authors.forename: Greg J
authors.initials: GJ
authors.lastname: Stanisz
mesh_terms: D000465:Algorithms; D000577:Amides / Q000737:chemistry*; D000588:Amines / Q000737:chemistry*; D000818:Animals; D014408:Biomarkers, Tumor / Q000737:chemistry*; D045744:Cell Line, Tumor; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods*; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D051379:Mice; D016513:Mice, SCID; D057054:Molecular Imaging / Q000379:methods*; D009374:Neoplasms, Experimental / Q000737:chemistry* / Q000473:pathology; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity
chemical_list: D000577:Amides; D000588:Amines; D014408:Biomarkers, Tumor
keywords: CEST; Lorentzian; aliphatic; amide; amine; chemical exchange saturation transfer; tumor